1. Field of the Invention
The present invention relates to a piston type compressor, in which fluid is compressed by means of reciprocating pistons connected to a swash plate. More particularly, it relates to improvements in the reciprocating pistons in the refrigerant compressor of an automotive air-conditioning system, such that both the weight of the pistons and abrasion to the pistons is reduced.
2. Description of Related Art
Variable capacity swash plate type compressors are known in the art. A typical conventional variable capacity swash plate type compressor is disclosed in Unexamined Japanese Patent Publication No. H7-189898, which disclosure is incorporated herein by reference.
Referring to FIG. 1, which depicts a variable capacity swash plate type compressor, a front housing 12 of the compressor is connected to the front end of a center housing 11. A rear housing 13 is connected to the rear end of center housing 11, with a valve plate 19 interposed therebetween. A cylinder block 11b is accommodated on the center housing 11. A plurality of cylinder bores 11a are equiangularly formed in the cylinder block 11b. A crank chamber 25 is defined in center housing 11 by cylinder block 11b. A drive shaft 14 is rotatably supported by means of radial bearing 22 disposed in front housing 12 and cylinder block 11b, respectively, in the crank chamber 25. A plurality of pistons 18 are reciprocally moveable and accommodated in cylinder bores 11a, respectively. A drive plate 15 is mounted on drive shaft 14.
The hinge mechanism is constructed with a pair of arms 15a of drive plate 15, connected to pins 16 of swash plate 17. Arms 15a are formed on drive plate 15 adjacent to the periphery thereof and project toward the rear direction. Each one of pins 16 includes a ball portion 16a which is rotatably engaged with arms 15a of drive plate 15. The peripheral portion of swash plate 17 is received via a pair of shoes 20 in recess 18d formed in the proximal portions of pistons 18, respectively.
The shoes 20 are slidable along the peripheral portion of swash plate 17. In this way, pistons 18 are retained at the peripheral portion of swash plate 17. As drive plate 15 rotates with drive shaft 14 synchronously, swash plate 17 is rotated with drive plate 15, via the hinge mechanism. Swash plate 17 is rotated with its surfaces inclined with respect to drive shaft 14 and slides in recess 18d via the pair of shoes 20, so that pistons 18 reciprocate in cylinder bores 11a in accordance with the inclination angle of swash plate 17.
A suction chamber 13a and discharge chamber 13b are defined by a partition 27 in rear housing 13. Suction ports 23 and discharge ports 24 are provided in valve plate 19. When pistons 18 reciprocate, refrigerant gas is sucked into cylinder bores 11a from suction chamber 13a through suction ports 23, respectively. After the gas is compressed in cylinder bores 11a, it is discharged into discharge chamber 13b through discharge ports 24. The difference between the pressure in crank chamber 25 and that in suction chamber 13a is adjusted by the opening or closing operation of the control valve mechanism (not shown). Consequently, the stroke of piston 18 is varied. The displacement of the compressor is controlled by regulating the inclination angle of swash plate 17.
In the above mentioned variable capacity swash plate type compressor, it is desirable to reduce the load that is applied to the compressor drive source, e.g., a vehicle engine. To accomplish this, piston 18 is preferably lightweight.
Therefore, each of the pistons 18 has a cylindrical body 18a thereof. A first aperture 18b and second aperture 18c are formed in the peripheral surface of cylindrical body 18a. First aperture 18b is formed nearer the piston head portion of piston 18 in comparison with second aperture 18c. In this arrangement, first aperture 18b protrudes from the edge of cylinder bore 11a into crank chamber 25 when piston 18 stays in bottom dead center.
The frictional force which is generated by the sliding of swash plate 17 within shoes 20 is transferred to piston 18, urging piston 18 to incline in a radial direction by the moment perpendicular to drive shaft 14 and to the longitudinal axis of piston 18.
As a result, first aperture 18b of piston 18 is easily caught on the edge portion of cylinder bore 11a. This causes noise and vibration in the compressor, and also abrasion of the piston 18.